TEAM 5: Characterization of the ANWR Ecosystem

TEAM 5: Characterization of the ANWR Ecosystem

Rabia Chaudhry, Christine Fanchiang, Breton Frazer, Sueann Lee, Yaa-Lirng Tu

Introduction

The Arctic National Wildlife Refuge is a diverse but fragile ecosystem. The 1002 region in particular, a coastal strip caught between the Brooks Range Mountains and the Beaufort Sea, is an intricate network of species and their surroundings that stand to be severely damaged by human activities. It is essential to establish a baseline of the ANWR ecosystem in order to create an assessment of the effects of oil drilling on its well-being and to take the proper precautions to preserve it.

In order to create a comprehensive model of the ecosystem, we have to set up the important parameters and components that define an ecosystem. Based on ecological models from multiple references, we have determined the main constituents of an ecosystem to include the following: geography structure and relief, climate, soils, hydrology, producers and consumers, decomposition and soil processes, energy and nutrient cycling, and interaction between terrestrial and aquatic communities (if relevant to the area of study). By developing a descriptive and quantitative model for each constituent we can compile the information for the structure and function of the ANWR ecosystem.

Geography

The Arctic National Wildlife Refuge spans 9.6 million acres and lies on the edge of the Artic Ocean and, bordered by Prudhoe Bay to the West and the Canada to the East. The 1002 area, 1.5 million acres of northeastern ANWR, lies on the Coastal Plain of ANWR and is situated in the 100 miles between the Aichilik River to the east at 142º 10' W and the Canning River to the west at 146º 15' W. It is trapped between the Brooks Range Mountains located at 69º 35' N and the Beaufort Sea at 0º 10' N, and its close proximity to the two ecoregions produces a variety of ecological conditions and habitats which support a wide spectrum of vegetation.

The entirety of ANWR spans many regions, including the Arctic coast, the tundra plain, the Brooks Range Mountains, and the Yukon basin forests. It contains over 20 rivers, including National Wild Rivers the Sheenjek, Ivishak, and Wind; North America's largest and most northerly alpine lakes Peters and Schrader; warm springs; lagoons; and glaciers. In the 1002 area, specifically, there are also many rivers that run northward and a few large lakes which freeze all the way to their bottoms by winter. Polygonal patterns on the ground across the region are formed by the seasonal thawing of the surface which will be explained in greater detail in the hydrology section. The disturbance of the surface tundra results in permanent alteration of the terrain, including the creation of ponds, ice wedges, vegetative cover and erosion.

Climate

The climate of Northern Alaska can be divided onto three different zones: Arctic Coastal, Arctic Inland and Arctic Foothills. Extending 20 km from the ocean, the 1002 area falls under the category of Arctic Coastal, which is characterized by cool summers and relatively warm winters, due to the impact of the ocean. Partially due to the rain shadow created by the Brooks Range just south of the coastal plain, the region has the lowest precipitation, 50 percent of which falls as snow. The air temperatures remain below freezing through most of the year and snow covers the ground surface for more than 8 months from October through April (Zhang, Osterkamp 1996).
Temperatures

Temperatures reach a high of about 86 degrees F in the summer (averaging about 41 degrees) yet drops to well below zero (averaging -4 degrees) in the winter. The global warming trend has already increased temperatures in the Arctic by 5 degrees F and 8 degrees in the winter since the 1960s, leading to shorter ice seasons, glacier melting, permafrost thaw, and increased precipitation. The inevitable change in climate may lengthen the growing season, but it will also alter the delicate ecological balance in ANWR (anwr.org).

Precipitation

Measuring precipitation in a wind-swept region, especially where the total quantity is small and more than 50 percent comes as snow, is a complicated problem. ANWR has an average rainfall of about 25cm, and solid winter precipitation for coastal areas averaged 15.3cm for the three years of study 1994-97. Out of this 34 percent of the precipitation sublimed (Sturm 2002).

During the winter months, virtually all precipitation falls in solid form. The low-growing vegetation and high wind speeds that characterize the domain allow significant wind redistribution of snow throughout the winter. This means that snow depths can be quite variable and, under appropriate conditions, some of the snow cover is returned to the atmosphere by blowing snow sublimation. Winter precipitation measurements do not exist in wind-blown arctic regions (Sturm 2002).
Snow cover

Snow cover possesses certain thermal properties which compete with air temperature on the ground thermal regime. It has high reflectivity and emissivity that cool the snow’s surface; snow cover is a good insulator that insulates the ground; and melting snow is a heat sink, owing to its latent heat of fusion (Zhang et al., 1997). In spite of the high albedo from spring and early summer snow and cloud cover, net radiation is positive throughout the year (Hare, F. K. 1972).

The microclimate of an environment, or the climate near the ground, is largely a function of energy exchange phenomena at the ground-air interface. The average maximum thickness of the seasonal snow cover varied from about 30cm along the Arctic coast to about 40cm inland for the period from 1977 through 1988 (Zhang et al., 1996a). The thickness of seasonal snow cover, however, can vary substantially on a micro scale due to the impact of wind, ground surface morphology, and vegetation. Along the Arctic Coastal Plain, the ground surface is relatively flat and mainly occupied by low-center polygons. Vegetation is poorly developed, and the region experiences high wind speeds during the winter months (Haugen 1982).

In this setting, the snow can be either blown away or well packed by strong wind, reducing the insulating effect. Inland, the ground surface becomes rough and vegetation changes significantly as a result of increased summer warmth. Wind redistributes the snow which is better trapped in the troughs and depressions created by rough micro relief and the taller vegetation. The trapped snowincreases the insulating effect of the seasonal snow cover, which, in turn, influences the permafrost conditions that determine vegetation of the area. On a monthly basis, seasonal snow cover warms the ground surface during winter months but cools it during the period of snowmelt. On an annual basis the seasonal snow cover definitely warms the ground surface. (Zhang et al., 1997)

In contrast with the Arctic coast, the Arctic inland and Arctic foothills feature lower wind speed, a very rough surface with tussocks, troughs and depressions, and well-developed vegetation. Snow can be interrupted and trapped by vegetation and rough surface, increasing the insulating effect and permafrost temperatures.
Effects of Global Warming

Climatic warming associated with elevated levels of greenhouse gases in the atmosphere is predicted to be greater in the Arctic than elsewhere, almost two to three times more than the global average (Osterkamp 1982). The impact of climatic warming on the Arctic ecosystem is uncertain, as are the feedback processes to potential changes in the exchange of greenhouse gases between the polar soil and atmosphere. This will be discussed further with relation to soil and the carbon cycle. One of the main reasons is that climatic conditions on the north slope of Alaska are not well understood owing to the sparsity of meteorological stations and discontinuity of observations.

Analyses of data collected by a number of studies done from the late 1940s onwards at and around Barrow and Prudoe Bay showed that the permafrost surface has warmed 2º to 4º C in the Alaskan Arctic over the last century (Lachenbruch and Marshall 1986; Lachenbruch et al., 1988). Since then, the rate of increase in temperature has accelerated greatly, to about 1º C per decade. Snow and shrubs form a positive feedback loop that could change land surface processes in the Arctic. The increased subnivian soil temperatues that are observed would produce conditions favorable to shrub growth (i.e. more decomposition and nutrient mineralization) (Strum et al., 2001). Aerial photographs taken of Alaska's North Slope during the 1940s offer some of the best evidence of such change: a dramatic increase in the growth of trees and shrubs in the Arctic.

Hydrology

Water Availability

The Arctic Coastal Plain may seem to be abundant in water resources, but in actuality, the low precipitation limits the amount of readily available water. Much of the available water resources come from snow melt, runoff, and rivers and lakes within the area. In arctic and subarctic areas, rivers typically carry 55 to 65 percent of precipitation falling onto their watersheds. The reason is that permafrost prevents the downward percolation of water and forces it to run off at and very near the ground surface. One of the consequences of the high runoff is that northern streams are much more prone to flooding. Another is that they have higher eroding and silt-carrying capabilities (A).

Critical to the control of water runoff in the north is the cover of moss and other vegetation of the tundra, bogs and forests. A thick layer of moss acts much like a sponge laid over the permafrost to slow down the movement of water across the ground surface.

Frozen Water Formations

One main source of water is in thermokarsts or thaw lakes. These lakes are actually thaw basins, low areas in the tundra where water from melting snow and ice collect. Thousands of square miles in the Arctic are covered by ground which has been segmented into what are called tundra polygons or ice wedge polygons. This pattern is caused by intersecting honeycomb networks of shallow troughs underlain by more or less vertical ice wedges. The ice wedges are formed when the ground contracts and splits in a manner analogous to the formation of cracks on the dry lake bed. This allows water to enter, and successive seasons of repeated partial thawing, injection of water, and refreezing cause the wedges to grow. As they do, the strata to either side are turned up to enclose the polygon, and a lake may form in the center with the raised troughs at the margins. Above the frozen region, unfrozen water saturation increases due to low hydraulic conductivity, which prevents the melting ice from draining, thus causing accumulation of water above it (E). During this process, pingos are sometimes formed, when the pressure from the contraction of the unfrozen water pushes it up until it collects and freezes under the root mat.

All of the thaw lakes studied were very shallow; even though the lakes could be several thousand feet long, most were no deeper than 10 feet (A).

Drainage patterns typically follow the troughs, and where they meet, small pools may form. These are often joined by a stream which causes the pools to resemble beads on a string -- in fact, this type of stream form is called beaded drainage. Thaw lakes tend to be elongated perpendicular to prevailing winds caused by subsurface currents. The waves caused by crosswinds may be eating away at the peat more aggressively along the edges creating a pattern of elongation that all arctic lakes share (A).

The amount of available water in the 1002 area has been estimated to be around 9 billion gallons (TAPS).

Water Usage in the 1002 Area

Water resources are limited in the 1002 Area. In winter, only about nine million gallons of liquid water may be available in the entire 1002 Area, which is enough to freeze into and maintain only 10 miles of ice roads. Although such exploration is conducted only in winter, snow cover on the 1002 Area is often shallow and uneven, providing little protection for sensitive tundra vegetation and soils. The impact from seismic vehicles and lines depends on the type of vegetation, texture and ice content of the soil, the surface shape, snow depth, and type of vehicle.

Oil companies are withdrawing surface water faster than it can be replenished, says Steve Lyons, hydrologist with the U.S. Fish and Wildlife Service (USFWS). When an ice road melts, the water runs over the surface into streams, usually outside the original watershed from which it was withdrawn, he explains. Because the 1000-ft-thick permafrost does not allow groundwater movement between water bodies, lakes are filled only by snowmelt and may take more than two years to refill after the permitted 15% of their liquid volume is withdrawn for ice road construction (G).

Surface water will also be used for potable purposes at manned facilities, equipment washing, tank cleaning, dust abatement on roads and workpads, and hydrostatic testing.

Permafrost

Examining the soil and water cycles of the 1002 region, one cannot ignore the presence of permafrost, or “permanently frozen soil,” which underlies 80% of Alaska and remains a central issue in the debate about oil drilling. Permafrost has been defined as frozen ground in which a naturally occurring temperature below 0° C (32° F) has existed for two or more years (A). On the North Slope, permafrost ranges in thickness from about 700 to as much as 2,240 feet thick, and may be as cold as -8° to -10° C.

Permafrost can be either thaw-stable or non thaw-stable, depending on the type and percentage water of the soil it is made of. Permafrosts in more fine-grained soils like loess (silty) tend to thaw, sink, and create thermokarsts more often. Permafrost thaws from heat input, such as global warming or human activity, as well as the clearing of vegetation which insulates the ground.

Permafrost is affected by road dust generated by traffic on unpaved roads; snow melt due to dust deposition can lead to flooding, ponding, and hydrological changes in oil. Continuing oil and gas exploration, development, and production, construction of a natural gas pipeline, the operation and maintenance of facilities, and other activities requiring road travel would add cumulatively to the volume of road dust generated on unpaved roads (A). Regions of ice which have been wind-dusted are likely to undergo localized melting earlier than the neighboring non-dusted ice (A).

There are three approaches to dealing with the permafrost problem in the construction practice. The first and most obvious is to avoid it entirely. The second is to destroy it by stripping the insulating vegetative cover and allowing it to melt over a period of years. This has the obvious drawback of requiring a considerable period of time to elapse before construction can begin, and even then, it is a good idea to excavate the thawed ground and replace it with coarse material.

The third approach, and one which is becoming more widespread, is to preserve it. This can be accomplished by building on piles to allow cold air to circulate beneath heated structures, by building up the construction site with gravel fill which insulates and protects the permafrost below, or by refrigeration to maintain low ground temperatures. This is done by utilizing thermal piles or freeze tubes, such as those used by the trans-Alaska pipeline. These devices are filled with a non-freezing liquid and act like coffee percolators. They are cooled during the winter months and draw heat from the ground to retard thawing during warm weather (A).

In nearshore areas, ice-bonded permafrost is probably present and must be considered in the design of an offshore pipeline. But nearshore ice-wedge permafrost under shallow water, particularly along a rapidly receding coastline, is even more critical for design. Oil pipelines placed in areas of ice-bonded or ice-wedge permafrost must be heavily insulated to limit thawing of permafrost. The best location for an offshore platform is at water depths of 6.5-65 feet, to minimize ice gouging. Beyond the 6.5 foot water depth the top of the ice-bonded permafrost generally is below the surface of the seabed. Inshore of the 18-foot bottom-depth contour, ice gouging is typically less than 1.6 feet (Y).

Soil

The Arctic Coastal Plain consists of marine (carried into seas by streams and beach erosion), fluvial (carried by flowing river water), alluvial (carried by river water that gradually loses velocity), and aeolian (carried by wind) deposits from the rising of the Arctic Sea on the plain in the mid/late Quaternary Age.

The Coastal Plain is dominated by lakes and poorly-drained soils, while the Brooks Range has less lakes and more well-drained soils (due to river flow). Poorly-drained soils mostly result from the predominance of permafrost, which restricts water flow in and out of the soil, as well as impermeable bedrock in more upland areas.